1. Field of the Invention
This invention relates to soaps suitable for skin and hair treatment and has particular reference to a novel antibacterial toilet soap which comprises 2,4,4'-trichloro-2'-hydroxydiphenylether and one or more organic phosphoric esters represented by the formula (I), ##STR3## wherein R represents an alkyl group having 8 to 20 carbon atoms, or a group of ##STR4## in which R.sub.1 is an alkyl group having 8 to 20 carbon atoms, R.sub.2 is a hydrogen atom or a methyl group, and n is an integer of 1 to 10; R' represents the same group as R, or a hydrogen atom or an alkali metal; and M represents a hydrogen atom or an alkali metal.
2. Description of the Prior Art
2,4,4'-Trichloro-2'-hydroxydiphenylether is a known compound which possesses a broad antibacterial spectrum for microorganisms such as Gram positive and negative bacteria, mold, yeast and the like. Moreover, the compound exhibits substantially reduced toxic and irritating effects upon the skin and mucous membrane of human beings. Because of such substantial advantages, the compound is useful as a good antibacterial agent for inhibiting any noxious microorganisms which would adhere to the skin and hair, and therefore, can be expected to find wide application to soaps, shampoos, detergents, cosmetics, ointments and similar articles.
However, such antibacterial compound or 2,4,4'-trichloro-2'-hydroxydiphenylether is encountered with the drawback that the compound when incorporated into any conventional soap bases causes the resulting soaps to discolor or become dark brown when they are exposed to sunlight. Although discoloration in the soaps does not induce adverse affects upon the anti-bacterial action of the compound, nevertheless it mars attractive appearance of the soap product and makes the user feel uneasy. This problem is detrimental to commercial acceptance of generally light-colored soaps. Accordingly, a need continues to exist for an antibacterial toilet soap which produces no color deterioration even upon exposure to sunlight.
In fact, various attempts have been made to reduce, retard or prevent discoloration in the soaps of the type described, and some reports on the problem have been made public. According to U.S. Pat. No. 3,284,362, an aromatic carboxylic acid or an alkali metal salt thereof is employed as a discolor-preventing agent in a soap composition. The use of a C.sub.8 -C.sub.22 substantially straight-chain fatty acid is disclosed in U.S. Pat. No. 3,625,903 and Japanese Patent Publication No. 47-20629. On the other hand, Japanese Patent Publication No. 52-43207 is concerned with color stabilization with the aid of organic acids such as malonic acid, citric acid and malic acid. It has now been found that satisfactory results cannot still be obtained by such prior art techniques.
The present inventors have made many studies concerning minimizing or avoiding color formation or discoloration in a variety of antibacterial soaps into which 2,4,4'-trichloro-2'-hydroxydiphenylether is incorporated. As a result of these studies, they have discovered that particular organic phosphorous compounds having the formula (I) exhibit excellent discolor-preventing characteristics and are suprisingly efficient in preventing the soaps from discoloration. The present invention bases its achievement upon this discovery.